Earthworms - July 12, 2006
Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County
Earthworms are valuable to gardeners because they consume and process organic matter converting it into plant-available nutrients. Worm burrows provide easy channels for root growth that are lined with readily available plant nutrients and provide air spaces where oxygen is available for plant roots. In addition, earthworms improve soil structure by mixing organic matter with deeper soil layers and excreting compounds that bind soil particles together. This activity increases the ability of soil to accept water and allows it to penetrate more deeply into the soil profile. Aristotle called earthworms “the intestines of the earth.”
There are over 1,800 species of earthworms which range in size from a few millimeters to a meter in length. The most common worms in North America, Europe, and Western Asia belong to the family Lumbricidae, which has about 220 species. Only a few of these are commercially available and are grown for fishing bait.
Nightcrawlers live in soil and are collected from fields and lawns at night. They are not often “farmed” commercially due to their slow reproductive cycle. Field worms also live in soil, are smaller, and also breed slowly. Manure worms (also called brandlings, red wigglers, or angleworms) and red worms live in organic debris and are the preferred types for commercial bait production and composting.
While considered primitive, the earthworm has well-developed nervous, circulatory, digestive, excretory, muscular, and reproductive systems. Earthworms breathe through their skin and must be in an environment that has at least 40 percent moisture (at least as damp as a wrung out sponge). If their skin dries out they cannot breathe and will die. Earthworms prefer a near-neutral soil pH. For these reasons, earthworms in Arizona are most common in riparian ecosystems (areas adjacent to flowing and standing water) and cultivated areas.
Instead of teeth, earthworms have a gizzard, like a chicken, that grinds the soil and organic matter they consume. Worm excrement is commonly called worm casts or castings. These soil clusters are glued together when excreted by the earthworm and are quite resistant to erosive forces. Castings contain many more microorganisms than food sources because their intestines inoculate the casts with microorganisms.
The earthworm's digestive tract is highly adapted to its burrowing and feeding activities. The worm swallows soil (including decomposing organic residues in the soil) or residues and plant litter on the soil surface. Strong muscles mix the swallowed material and pass it through the digestive tract as digestive fluids containing enzymes are secreted and mixed with the materials. The digestive fluids release amino acids, sugars, and other smaller organic molecules from the organic residues. In addition, the castings contain living protozoa, nematodes, bacteria, fungi, and other microorganisms as well as partially decomposed plant and animal materials.
Earthworms become sexually mature when the familiar band (the clitellum) appears around their body, closer to their mouth. Each worm with a clitellum is capable of mating with other worms and producing cocoons that contain baby worms. Cocoons are lemon shaped and slightly smaller than a pencil eraser. The eggs hatch after about three weeks, each cocoon producing from two to twenty baby worms (four is the average).
Gardeners often see night crawlers and field worms when working garden soil, during irrigation, and in soil around active compost piles. More enthusiastic gardeners use manure worms and/or red worms to make compost. This is called vermiculture or vermicomposting and requires some care to maximize compost production and sustain/increase worm populations. Many vermiculture resources are available in print and on-line. North Carolina State University has an excellent web site with vermicomposting information and suggested reading at: catawba.ces.ncsu.edu/copubs/ag/special/worm/001/.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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